Sintered cobalt-rare earth intermetallic product

ABSTRACT

A process for preparing novel sintered cobalt-rare earth intermetallic products which can be magnetized to form permanent magnets having stable improved magnetic properties. A cobalt-rare earth metal alloy is formed having a composition which at sintering temperature falls outside the composition covered by the single Co5R intermetallic phase on the rare earth richer side. The alloy contains a major amount of the Co5R intermetallic phase and a second solid CoR phase which is richer in rare earth metal content than the Co5R phase. The specific cobalt and rare earth metal content of the alloy is substantially the same as that desired in the sintered product. The alloy, in particulate form, is pressed into compacts and sintered to the desired density. The sintered product is comprised of a major amount of the Co5R solid intermetallic phase and up to about 35 percent by weight of the product of the second solid CoR intermetallic phase which is richer in rare earth metal content than the Co5R phase.

United States Patent [191 Anthony et al.

il 11 3,905,840 [4 1 Sept. 16, 1975 CORROSION RESISTANT ALUMINUM ALLOYS Inventors: William H. Anthony, 70 Hilltop Road; James M. Popplewell, 67 Edgewood Road, both of Guilford, Conn.

Filed: Sept. 18, 1974 Appl. No.: 507,017

Related US. Application Data Division of Ser. No. 451,074, March 14, 1974.

US. Cl 75/141, 75/148; 138/Dig. 6;

148/34 Int. Cl. C220 21 02 Field of Search 75/138, 141, 142,143,

75/146,147, 148; 138/177, Dig. 6; 148/32, 32.5, 34

[56] References Cited UNITED STATES PATENTS 3,219,492 11/1965 Anderson et al 75/138 3,639,107 2/1972 Thompson 75/138 Primary Examiner Richard 0. Dean Attorney, A g'ent, or Firm Charles E. Sohl [5 7 ABSTRACT A corrosion resistant aluminum alloy based on' commercial purity aluminum with deliberate additions of silicon and manganese and with a restricted iron content. The silicon and manganese ranges are controlled to provide an aluminum-silicon solid solution and to restrict or eliminate cathodic particles which have been found to cause pits. The alloy is highly resistant to corrosion, especially in environments where the alloy comes into contact with impure water.

7 Claims, 1 Drawing Figure LEGEND 1 P. rn/vc 1 PVE/GHT LOSS AVERAGE P/7 [)EPTH M/Ls WEIGHT Loss M/LL/GRAMS PER C EXPOSURE 77/145 /A/ 0/1 vs BACKGROUND '01 THE INVENTION! Many industrial processes result in the formation of a large amount of waste steam. Economic considerations require that the heat content of this steam should be recovered by condensing the steam. This condensation process is performed by passing the steam over metal tubes through which cooling water is passed. The cooling water is commonly impure, and contains impurities which cause severe corrosion problems and thereby add to the expense of the industrial process. Such condensors contain large quantities of tubing and represent a large potential market for any alloy which can withstand the corrosion effects of the cooling water. The preferred materials at present are stainless steel, and admiralty brass. Unfortunately, materials used heretofore in condensor applications have not been entirely satisfactory when considered from a price-performance viewpoint. Aluminum has not received much consideration because previously considered alloys havenot had an adequate combination of resistance to pitting and general corrosion. a

Many other industrial processes are also candidates for the application of a more corrosion resistant tubing of moderate cost. Examples include oil refinery and general chemical industry piping and tanks, irrigation equipment for agriculture, and automotive radiator applications. I I, i a

' 1 SUMMARY OF THE INVENTION The composition of the alloy of the present invention in the'following'description of the preferred embodiments is givenin Weight percentages unless otherwise specified. a

The broad and preferredcomposition limits for the alloy of the present invention are given in Table I- below: i

' TABLE I y 3 Broad Preferred Silicon 0.05-05 I 0.15 0.25 Manganese... .2 0.8' 0.3 I -0.6 Iron .0 '0.2 0.0 ,0.08 Chromium. .0 0.1 3 0.0 -0.05 Magnesium .0 0.3 0.0 0'.l .Copper .0 0.1 0.0 0.05

Titanium... .0 0.05 0005-0015- Zinc 0.0 0.1 0.0 -0.05

The essential components of the alloy are manganese and silicon. The remaining elements may be present as impurities up to the level shown in Table I. Titanium may be present asa purposeful addition for grain refinement of the alloy. The zinc has not been found to have any detrimental effects on the corrosion behavior of the'alloy and its level has been chosen to permit theuse of zinc bearing scrap in the production of the alloy. Naturally, any of the foregoing impurities may be present in levels as low as .001

A major cause of pitting corrosion in aluminum alloys is the presence of particles in the alloys which are cathodic or anodic to the matrix of the alloy. Such particles act to set up galvanic cells when the alloy is in a conducting medium. Such cells act as initiation sites for the formation of pits. Particles which are likely to cause pittinginclude; silicon, FeAl CUAlg,

MnAl and a(AlFeSi). In the course of the present research it was found that the presence of a cathodic particle of FeAl in a 6061 Alloy could lead to the formation of a pit in as little as one hour when the alloy was exposed to flowing tap water at a temperature of 30 C.

The alloy composition of the present invention has been selected on the basis of the constitutional relationship which has been derived for the aluminummanganese-silicon-iron quaternary system by H. W. L. Phillips, Journal of the Institute of Metals, Vol. LXIX, 1943. From this phase diagram it appears that the presence of about .4% manganese will surpress the formation of the FeAl particles. However, particles of a(AlFeSi) remain. For this reason the iron concentration in the present invention has been limited, since a(AlFeSi) particles arealso detrimental to the corrosion behavior of aluminum alloys, although to a much lesser degree than FfiAlg particles.

Other research has indicated that the pitting resistance of aluminum can vbe greatly improved by the introduction of silicon, provided that the silicon is in solid solution. The concentration range over which the silicon will remain in solid solution is largely dependent upon the iron and manganese concentrations, and the presence of magnesium. The silicon levels of the alloy .of the present'invention have been chosen in light of these considerations.

The preceedingdiscus'si'on of the present invention will bebetter understood-through consideration of the following illustrative examples:

EXAMPLE 1 C. No addition The castings werehomogenized at 1100 F for 16 .hours and were air cooled. The ingots were then scalped and hot rolled from 1.5 to .25" at a starting hot rolling temperature-of 825 F. Theingots were then coldrolled to 0.040 gage and flash annealed at l100. F for 10 minutes. After the flash annealing the samples were cold rolled. 25% to 0.030 gage.

Samples fromtthese three-alloys were cleaned and then exposed to flowing New Haven tap water at a temperature of 30 C which was replenished once a week. A sample of Alloy 3003 was used as a control. After 60, 120 and 180 days, samples were removed and analyzed for weight loss and pit depth. The data is displayed in Figure 1. These results demonstrate the definite superiority of the alloy of the present invention over high purity aluminum and the commercial alloy, 3003 control sample. It is evident that a combination of manganese and silicon results in an alloy superior in both overall corrosion rate and pit depth. Table II shows the approximate analysis of the water used in the examples.

TABLE II WATER ANALYSlS (PPP) A1 CONDENSER TUBING PROJECT was replenished every 12. hours. An approximate analysis of the water used is given in Table 11.

Examination of the corrosion data which is presented in Table 111 indicates that there is a type of synergistic effect on the pitting resistance over certain ranges of silicon and manganese. The optimum manganese level apparently lies between .4 and 1.0% and preferably near .4% while the optimum silicon level is at least .2%. The presence of .2% chromium has an adverse effect on the pitting resistance as does the presence of 1.0% magnesium, while manganese has a beneficial effect up to .6% but detrimental at Test with Intermittent Refreshment with New Haven Tap Water Refreshment Once a Week Example 1 employed a test in which the water was changed only once a week and it is evident that over a period of one week the chloride concentration decreases significantly. Because of the corrosive effect of chloride ions, subsequent tests were performed using continuous replenishment of the tap water in order to increase the severity of the test.

EXAMPLE II A series of experimental-ingots were cast using a high purity aluminum base but containing from .05 to .063% iron. The composition of these alloys is given in Table III along with 60 day corrosion data.

TABLE III CORROSION TEST RESULTS AND SPECTROSCOPIC ANALYSES ON EXAMPLE 1] ALLOYS AFTER 60 DAYS EXPOSURE TO NEW HAVEN TAP WATER Percentage Composition Pit Depth (mils) Weight Loss Fe Si Mn Cr Mg Mean Max mlgms/cm .056 .11 .43 15.0 22.5 12.8 .051 .23 .31 8.4 17.8 15.1 .055 .23 .45 8.8 15.3 15.4 .053 .10 .64 10.2 19.7 14.2 .050 .03 1.0 13.3 20.2 17.6 .061 .10 .63 .20 13.2 18.0 13.1 .061 .098 .61 .21 1.04 16.7 22.4 10.3 3003 Control 27.1 17.7

*27.1 mill thick coupon was perforated the 1% level. Therefore 0.8% seems to be the cut off point in usefulness. The detrimental effect of magnesium is due to the depletion of the solid solution concentration of silicon by the formation of magnesium silicide. Because the thickness of the 3003 control sample was less than the thickness of the other samples, and complete perforation occurred, it is not possible to accurately compare the pitting resistance of the 3003 control sample with the experimental alloys, however, examination of the samples indicated that the pitting of the 3003 sample was approximately twice as severe as the pitting of the best sample of the present invention.

EXAMPLE lII Three alloys having a base composition of .l% silicon and .6% manganese were cast and processed to .050 sheet according to the procedure described in Example 11. The purpose was to determine whether or not pitting was effected by varying the iron content of the alloy. An additional purpose was to investigate the effect of the addition of titanium diboride as a grain refiner on the pitting performance. The alloys were exposed to New Haven tap water as described in Example 11. The results are shown in Table IV and indicate that the alloy consisting of deliberate additions of .l% silicon and .6% manganese perform approximately as well from a pitting standpoint after exposure of 60 and days, regardless of whether the iron content is .01 or .063

In view of the well known highly detrimental effect of iron on pitting resistance of aluminum alloys, the efficacy of the manganese addition is clearly demonstrated. The addition of the titanium diboride in an amount sufficient to be effective as a grain refiner had no detectable effect on the pitting resistance of the alloy.

TABLE IV CORROSION TEST RESULTS AND SPECTROSCOPIC ANALYSES OF EXAMPLE 111 ALLOYS EXPOSED FOR VARIOUS TlMES UP TO 180 DAYS IN NEW HAVEN TAP WATER Weight Loss Pit Depth (mils) mlgms/cm Percentage Composition 60 Days 120 Days 180 Days 60 120 180 Fe Si Mn Ti B Mean Max Mean Max Mean Max Days Days Days EXAMPLE IV This invention may be embodied in other forms or The alloys of the present invention have moderate carried out other Ways wlthout depamng from the mechanical properties. Alloys having compositions as listed in Table V were cast and processed according to the process described in Example 11. The final cold reduction was 30% and the resultant mechanical properties are listed in Table V.

The alloys of the present invention have a wide potential area of usefulness, encompassing almost any application in which a metallic article must come into contact with relatively impure water or other aqueous media. Typical of such applications are tubing or piping for the flow of aqueous media and heat exchangers for the transfer of heat to or from an aqueous medium. The alloy of the present invention is particularly suitable for the fabrication of thin wall tubing, as for example welded tubing fromed from metal strips. Such tubing would normally have a wall thickness of from 0.02 to .375 depending upon the tube diameter, and a diameter of from A2" to 16". Of course, thick wall tubing and piping may be fabricated having a wall thickness of as much as 1.0. The alloy of the present invention may also be used in the fabrication of items such as tube sheets, and tube spacers and supports. In general, the alloy of the present invention is useful whenever aqueous corrosion problems are encountered, whether in power plants of petroleum refineries.

spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims and all changes which come within the meaning and range of equivalency are intended to be placed therein.

What is claimed is:

1. A corrosion resistant aluminum alloy tube for the transport of aqueous solutions resistant to pitting and corrosion in an aqueous environment having a diameter of from 0.125 to 16 and a wall thickness of from 0.02 to 0.375, said tube being formed from an aluminum base alloy consisting essentially of from 0.05 to 0.5% silicon, wherein the silicon is present in solid solution, from 0.2 to 0.8% manganese, from 0.001 to 0.2% iron, from 0.001 to 0.1% chromium, from 0.001 to 0.1% magnesium, from 0.001 to 0.1%

copper, from 0.001 to 0.05% titanium, from 0.001 to 0.1 zinc, balance aluminum.

2. A corrosion resistant aluminum alloy tube as in Claiml wherein the silicon is from 0.15 to 0.25%.

3. A corrosion resistant aluminum alloy tube as in Claim 1 containing less than 0.4% manganese.

4. A corrosion resistant aluminum alloy tube as in Claim 1 wherein the iron content is from 0.001 to 0.08%.

5. A corrosion resistant aluminum alloy tube as in Claim 1 containing from 0.001 to 0.05% chromium, from 0.001 to 0.05% copper, from 0.005 to 0.015% titanium and from 0.001 to 0.05 zinc.

6. A corrosion resistant aluminum alloy tube as in Claim 1 wherein the magnesium content is less than 0.01%.

7. A corrosion resistant aluminum alloy tube as in Claim 1 wherein said tube is a welded tube.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION a PATENT NO. 3,905,8HO

DATED I September 16, 1975 V I William H. Anthony and James M. Popplewell It is certified thaterror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: O

In the heading insert ---Assignee: Swiss Aluminium Limited, Chippis, Switzerland--.

' In Column 2, line 58, "0. 61" should read --O. 6%--.

In Column 3, line 61, "The" should read ---'Ihey---.

. In Column 5, line 30, the word "fromed" should read --formed--;

In Column 5, line 2, the word "of" should read ---or-.

; Engncd and Sealed thus nd Day of March 1976 [SEAL] Q Arrest:

i RUTH c. MASON C.MARSHALL DANN Arresting Officer 1 Commissioner ofParenrs and Trademarks oi i 

1. A CORROSION RESISTANT ALUMINUM ALLOY TUBE FOR THE TRANSPORT OF AQUEOUS SOLUTIONS RESISTANT TO PITTING AND CORROSION IN AN AQUEOUS ENVIROMENT HAVING A DIAMETER OF FROM 0.125 TO 16" AND A WALL THICKNESS OF FROM 0.02 TO 0.375", SAID TUBE BEING FORMED FROM AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF FROM 0.05 TO 0.5% SILICON, WHEREIN THE SILICON IS PRESENT IN SOLID SOLUTION, FROM 0.2 TO 0.8% MANGANESE, FROM 0.001 TO 0.2% IRON, FROM 0.001 TO 0.1% CHROMIUM, FROM 0.001 TO 0.1% MAGNESIUM, FROM 0.001 TO 0.1% COPPER, FROM 0.001 TO 0.05% TITANIUM, FROM 0.001 TO 0.1% ZINC, BALANCE ALUMINUM. 